As one of vehicles, which are driven by electric energy stored in a secondary battery, a vehicle (plug-in chargeable vehicle) is known as being capable of charging the secondary battery by using an electric power source provided outside the vehicle. As the plug-in charge type vehicles, for example, EV (electric vehicle) and PHV (plug-in hybrid vehicle) are known. Patent documents 1 and 2 disclose a technology of charging a secondary battery of a plug-in vehicle. According to this technology, in case of charging the secondary battery by an electric power source provided outside the vehicle, a radio signal indicating a charge amount of the secondary battery is transmitted from the vehicle to a mobile terminal and information about the charge amount is indicated on a display of the mobile terminal.    Patent document 1: JP 2008-247080A    Patent document 2: JP 2004-048900A
This technology is proposed to be applied to a dedicated short range communications (for example, infrared communications, Bluetooth, weak radio communications in LF band and UHF band used in keyless entry systems). As a result of the study, the following problems are found.
In the short range communications, the mobile terminal will not be able to receive the radio signal indicating the charge amount if a user carrying the mobile terminal gets off and leaves the vehicle. It is therefore desired that the user carrying the mobile terminal can estimate the charge amount by way of the mobile terminal even after leaving far away from the vehicle. The mobile terminal is required to receive the signal indicating the charge amount from the vehicle at least once for estimating the charge amount. If the signal indicating the charge amount is persistently transmitted from the vehicle as long as the mobile terminal is present within a range, in which it is possible to communicate with the vehicle, however, the electric power consumed for such communications will increase.
Further it is likely in the plug-in charge type vehicle that an electric power supply cable for connecting the secondary battery and the outside power source is forgotten to be disconnected. The user of the vehicle should normally disconnect the power supply cable connecting the secondary battery and the outside power source, and then gets in and starts to drive the vehicle. However, the user often forgets it and starts to drive the vehicle. In case of the short range communications, it becomes possible again to establish communications between the mobile terminal and the vehicle when the user carrying the mobile terminal comes back from the remote place and gets in the vehicle. It is configured transmit a signal indicating a state of connection of the power supply cable, which is for connecting the secondary battery and the outside power source, from the vehicle to the mobile terminal when the communications is resumed, and provide notification of warning to the user by the mobile terminal when the signal indicates that the electric power supply cable is still being not disconnected. The notification is sometimes not effective in a period from resumption of communications between the mobile terminal and the vehicle to start of travel of the vehicle.
As a result of study about estimation of the charge amount of the vehicle by the mobile terminal, it is found that, since the charge amount is notified at time irrespective of state of charge of the vehicle according to the technology disclosed in the patent documents 1 and 2, the notification is sometimes inappropriate to estimate the charge amount by the mobile terminal. For example, the mobile terminal is likely to transmit frequently inquires to the vehicle even though it is readily possible to estimate the charge based on a persistent increase of the charge amount at a constant rate. Such communications is wasteful. Further, even if the power supply capacity of a charger, which supplies the vehicle with electric power, changes greatly, the charge amount is not notified in some cases. In this case, the charge amount estimated by the mobile terminal differs greatly from the actual charge amount.